For some time, conventional paging services have been able to transmit one-way, unacknowledged messages to small battery powered receiving units, which are commonly known as pagers or beepers. Pagers are typically used by people who need to be able to receive messages when they are away from their home or office. To accommodate those who need to receive messages when traveling outside their local area, paging companies also provide regional and national paging services.
Basic paging services utilize numeric pagers, which are designed to receive and display a series of numbers. In most cases, the numbers are entered by the person calling the pager, and indicate the telephone number that the paging customer should call in order to respond to the page. More sophisticated paging services accommodate alphanumeric pagers, which are capable of receiving and displaying short messages that include a series of alphabetic and/or numeric characters. These are especially useful for physicians, salespeople, and others who need or want to receive information in addition to the simple telephone numbers displayed by numeric pagers.
Recent technology has also provided pagers, or more precisely, message receivers, that can be plugged directly into personal computers (PCs). These message receivers allow PCs to receive brief electronic mail messages and other types of information, including non-priority messaging such as news and weather. The messages may be displayed on the computer's display and/or stored for future use.
One obstacle associated with one-way paging networks is that the pagers are "receive only" devices and, as such, cannot transmit a message to the sender acknowledging receipt of the message. Because the messages cannot be acknowledged, paging networks include several features that improve the reliability of message delivery by increasing the likelihood that a pager will accurately receive its messages. These features include using simultaneous, high powered transmissions from multiple, in-phase transmitters, and sending messages more than once. For one-way short message transmission, paging companies claim reliable message delivery rates of up to 99%.
In order to further improve reliability, some paging networks also include a message sequence number with the transmitted message. The pager displays the message sequence number along with the message. If the user notices a gap in the sequence numbers of recently received messages (e.g., [01 ], [02], [04], [05], where [03] is missing), the user can manually dial the paging network over a telephone and request that the missing page or pages be retransmitted.
Inasmuch as pagers are used to allow communication with a person who is away from their home or office, paging devices must operate from batteries. Because batteries have a finite life, measures have been taken to extend the battery life, therefore, extending the amount of time a pager can operate without replacing or recharging its battery. An advantage of one-way paging is that because the pager is "receive only" and does not transmit messages, the battery in the pager lasts a relatively long time (perhaps a month or more, depending on the number of messages received).
Current one-way paging protocols attempt to conserve battery power by allowing pagers to spend most of their time in a sleeping or idle state. An example of such a protocol is the Post Office Code Standardisation Advisory Group (POCSAG) protocol for the delivery of one-way messages from the paging network to the pager, which was defined by the British Post Office and adopted as an industry standard.
The POCSAG protocol provides for battery savings by combining eight data frames into a single batch for transmission, and by enabling the receiver to occasionally sample the radio frequency rather than doing so continuously. In the POCSAG protocol, each transmission begins with a preamble, called the synchronization word. The preamble consists of at least 576 bits containing a special sequence of ones and zeros, which are sampled by the pager and used to synchronize the pager to the paging network. The synchronization word is followed by one or more batches of messages. Within each batch are eight frames numbered from 0 to 7. Each pager is assigned to one of the frame slots and need only listen to its specific frames slot within a batch of messages.
When a pager is first turned on, it looks for a synchronization word from the paging network. During its idle mode, the pager turns on every few seconds to receive one word of data per batch at the time a synchronization word is expected to be heard, based on the last reception of a synchronization word. When the synchronization word is detected, the pager decodes the addresses within the appropriate frame of the batch. If its address is present, the pager proceeds to decode the following message and then returns to the idle mode, until the time when the next synchronization word is expected. If no message is destined for the pager, the pager goes back to sleep. Every eight batch periods, the receiver switches on for one complete batch to ensure that it is properly synchronized. This allows the pager to recover from a temporary loss of signal from the network. In essence, the primary battery conservation measures employed in a one-way paging network using the POCSAG protocol is to keep the pager in an idle or sleeping mode whenever possible.
The Federal Communications Commission (FCC) has recently released a portion of the radio spectrum for Narrowband Personal Communications Services (PCS). With the release of this radio spectrum, the FCC has auctioned ten nationwide paging channels, some of which are paired, and some of which are not. In either case, paging service providers intend to use many of these channels to provide two-way paging services. In a two-way paging system, the pager includes not only a paging receiver but a small packet radio transmitter that is able to send short messages from the pager back to the paging network.
The presence of the transmitter in the pager makes it possible for the pager to positively acknowledge receipt of each message by transmitting a signal back to the paging network. If the network does not receive confirmation of message receipt by the paging recipient, then the network may be configured to transmit the message again. Further, the reverse channel, from the pager to the network, can also be used to send short electronic mail messages from the pager to the network, which forwards the message to the intended recipient.
However, once a transmitter is incorporated into a pager, and the two-way pager begins to transmit data, the pager's battery life will be reduced due to the power consumed by the transmitter. If two-way paging systems utilize protocols similar to those used in conventional two-way packet radio networks, the pagers will acknowledge each message that is received from the paging network. This means that when a message is received by the pager, the two-way pager transmits a short data burst back to the paging network indicating that message was received (or perhaps garbled, requiring a retransmission). Although acknowledging each message enhances the reliability of the paging system, the transmission of the acknowledgment will decrease the battery life of the two-way pager. Indeed, acknowledged paging could drastically reduce the 30 day battery life of today's pagers down to less than one week for two-way pagers (depending upon the traffic load delivered to the pager).
The reduction in battery life is even more severe when a two-way paging unit is used in conjunction with portable or hand held computers. For example, existing handheld computers may have battery lives of 4 to 8 hours. However, when a radio transmitter is connected to the computer, the battery life could be significantly reduced. Therefore, there is a need in the art for a method of improving battery life expectancy for two-way pagers, including a method for operating a two-way messaging system in order to reduce the use of the pager's transmitter whenever possible, without significantly impacting the reliability or timeliness of message delivery.
In addition, the unnecessary transmission of administrative or overhead messages decreases the effective capacity of the network. Therefore, there is a need in the art for a method for operating a two-way messaging system in order to minimize the amount of air time devoted to sending administrative messages back and forth, thereby increasing the effective capacity of the network and potentially lowering any air time charges billed to the user.